1. Field of the Invention
The present invention relates to a housing. More particularly, the present invention relates to a housing of a projection apparatus.
2. Description of the Related Art
With the rapid progress in opto-electric and projection technologies, wide screen projection apparatus having high display quality and high resolution are in great demand. To achieve a higher display quality and provide a high brightness, a high-power light source is often required. When a high-power light source is used in a projection apparatus, more heat is produced. Thus, the interior of the projection apparatus as well as the housing may be over-heated. To prevent the housing of the projection apparatus from over-heating, the housing must be properly insulated so that the housing is maintained at a moderate temperature throughout the operational period.
FIG. 1 is a diagram of a conventional housing for a projection apparatus. As shown in FIG. 1, the housing 100 includes an outer casing 110 and a beat conductive element 120. The heat conductive element 120 is made of a highly conductive material such as aluminum or copper. The heat conductive element 120 is disposed on an inner wall 110a of the outer casing 110 and reflects light from a light source 130 so as to prevent the light source 130 from directly illuminating on the inner wall 110a of the outer casing 110 that may cause over-heat of the outer casing 110. Furthermore, due to a better thermal conductivity of the heat conductive element 120, the outer casing 110 is evenly heated. Nevertheless, due to direct contact, part of the heat absorbed by the heat conductive element 120 is conducted to the outer casing 110, which still results in an increase of the temperature of the outer casing 110.
FIG. 2 is a diagram of another conventional housing for a projection apparatus. As shown in FIG. 2, the housing 100′ includes an outer casing 110, a heat conductive element 120 and a layer of foam 140. The main difference of this design from the housing illustrated in FIG. 1 is that the layer of foam 140 (having a thermal conductivity k=6.06×10−2 W/m*K) is disposed between the outer casing 110 and the heat conductive layer 120 of the housing 100′. The layer of foam 140 is an insulating layer that prevents the conduction of heat from the heat conductive element 120 to the outer casing 110. Although the layer of foam 140 with a lower thermal conductivity can reduce the amount of heat conducted to the outer casing 110, the heat-insulating performance of the layer of foam 140 is still quite limited. Furthermore, the layer of foam 140 is expensive, and manufacturing a thin layer of foam with high quality is difficult. Moreover, the thickness of the layer of foam 140 has to be increased if a better insulating effect is desired. However, increasing the thickness of the layer of foam 140 also increases system impedance and assembling instability.
Aside from the aforementioned thermal insulating designs, heat-dissipating techniques are often deployed to prevent over-heating of the housing. For example, an air flow is forced through a gap between the light source and the outer casing to cool down the outer casing and lower the casing temperature. However, if the gap between the light source and the outer casing is too narrow or there is too much obstruction to the air flow, the cooling effect on the outer casing will be significantly compromised. Furthermore, the cooling air for cooling the outer casing may be preheated by some other heat-emitting elements inside the housing, thereby limiting the ultimate cooling effect.